Method and apparatus for generating and displaying location-specific diagnostic information using an implantable cardiac stimulation device and an external programmer

ABSTRACT

Location-specific diagnostic information is detected and recorded by the cardiac stimulation device for subsequent display using the external programmer device. The diagnostic information includes location-specific event records, counters and IEGM signals. The event records include event codes that distinguish among events occurring in the four chambers of the heart, such as sensed or paced events occurring within the left or right atria or the left or right ventricles. The counters separately count events occurring within the chambers of the heart. The IEGM signals are separately detected within the four chambers of the heart using a multiple sensing lead arrangement. The location-specific event records, counters and IEGM signals are ultimately transmitted to the external programmer, which displays graphic representations of the diagnostic information. The event records are displayed using distinct event marker icons which distinguish among the four chambers of the heart. The distinct event marker icons are displayed along with location-specific IEGM displays or surface ECG displays to permit a physician operating the programmer to easily identify the specific chambers of the heart in which events the occurred. Additionally, the programmer displays the values of the various counters to provide, for example, a set of location-specific histograms. The diagnostic information detected and recorded by the stimulation device and displayed by the external programmer device may further distinguish among events detected at multiple locations within each chamber of the heart. Method and apparatus embodiments are described.

[0001] This application is a divisional of copending application Ser.No. 09/822,887, filed Mar. 30, 2001.

FIELD OF THE INVENTION

[0002] The invention generally relates to implantable cardiacstimulation devices and to external programmers used in connectiontherewith and in particular to methods and apparatus for processing anddisplaying event markers and other diagnostic information detected by animplanted device.

BACKGROUND OF THE INVENTION

[0003] A wide variety of implantable cardiac stimulation devices areprovided for surgical implantation into patients. One common example isthe cardiac pacemaker. Another is the internal cardioverterdefibrillator (ICD). Implantable devices are often configured to be usedin conjunction with an external programmer that allows a physician todisplay information detected by the implanted device. For example, theexternal programmer may operate to display electrical cardiac signalsdetected by the implantable device in the form of intracardiacelectrograms (IEGMs). An IEGM is a graphic depiction of electricalsignals emitted by active cardiac tissue as detected by electrodesplaced in the heart. The electrical signals are digitized and recordedwith the implanted device along with an indication of the date and time,then transmitted to the external programmer for display thereon, perhapsduring a subsequent follow-up session with the physician. Alternatively,the implanted device is controlled to transmit the IEGM signals inreal-time during the follow-up session. The external programmer may alsobe configured to receive real-time surface electrocardiogram (ECG)signals from an external ECG detector, perhaps for display along withcontemporaneous real-time IEGM signals transmitted from the implanteddevice.

[0004] The implanted device may also be configured to detect variousevents, such as paced and sensed events, and to generate event codesrepresentative of the events for transmission to the externalprogrammer. The event codes are detected and stored in the implanteddevice along with the corresponding IEGM signals and the date and timefor subsequent transmission to the external programmer or are detectedand transmitted to the external programmer in real-time along withreal-time IEGM signals. The external programmer generates event markericons based on the code and displays the icons along with either IEGMsignals, ECG signals, or both. Exemplary event markers are: P for asensed event in the atria; R for a sensed event in the ventricles; A fora paced event in the atria, and V for a paced event in the ventricles.Along with the event markers, the programmer may also display variablelength horizontal lines representative of the length of atrial andventricular refractory periods associated with the events along withnumerical values indicative of measured intervals between atrial andventricular events, based on still further information recorded andtransmitted by the implantable device. The external programmer may alsodisplay additional information received from the implanted device suchas numerical information identifying the heart rate and the duration ofventricular and atrial refractory periods. Also, the display may provideother event markers as well, such as event markers indicating modeswitching events. The implanted device may also maintain counters forcounting various events, such as paced and sensed atrial and ventricularevent counters, for subsequent transmission to and display using theexternal programmer.

[0005] An exemplary surface ECG display, along with event markers, isprovided in FIG. 1. More specifically, FIG. 1 illustrates three ECGcomplexes (denoted 2, 4 and 6), along with P and R event markersindicating that the atrial and ventricular events are both intrinsicevents. For both the P and R events, the display also includeshorizontal lines adjacent thereto that indicate the length of thecorresponding refractory period. Although not shown in FIG. 1, theexternal programmer may display additional information received from theimplanted device such as IEGM signals.

[0006] Such displays of event markers and counters are helpful inpermitting the physician to analyze the operation of the implanteddevice and to diagnose arrhythmias, if any, within the patient. U.S.Pat. No. 5,431,691 to Snell et aL entitled “Method and System forRecording and Displaying a Sequential Series of Pacing Events” providesa description of the operation of an exemplary pacemaker and externalprogrammer including a detailed description of the generation,transmission and display of IEGM data and event markers. U.S. Pat. No.5,431,691 to Snell et al. is incorporated by reference herein.

[0007] Although the typical event codes and counters maintained byimplantable devices and the typical event marker icons displayed byexternal programmers are quite helpful to the physician, room forimprovement remains. In particular, state of the art implantable devicesare being developed utilizing multiple sensing/pacing leads for pacingor sensing at multiple locations within the heart. For example, separateleads may be provided to the left and right atria, as well as to leftand right ventricles. In other cases, a single atrial lead may becapable of sensing and pacing in both the left and right atria, and asingle ventricular lead may be capable of sensing and pacing in the leftand right ventricles. Devices are also being developed which permitsensing or pacing at two or more locations within a single chamber.Eventually, highly sophisticated devices may be developed which permitsensing and pacing at a large number of locations within each chamber ofthe heart. As can be appreciated, when using such systems, theaforementioned conventional event codes, counters and event markericons, which typically distinguish only between the atria and theventricles may not be sufficient. Consider again the display of FIG. 1.The intrinsic events of the ECG complexes 2 and 6 may have been detectedonly within the right atrium and ventricle whereas the intrinsic eventsof the ECG complex 4 may have been detected only within the left atriumand ventricle. Yet, the events markers indicate no such distinction beenthe left and right chamber events. Moreover, because the complexesthemselves are derived from a surface ECG, rather than an IEGM, thecomplexes contain no polarization information that might permit thephysician to distinguish between the left and right chamber events.

[0008] Accordingly, there is a need to develop enhanced event codes,event marker icons and event counters which accommodate implantabledevices capable of separately sensing and pacing in the left or rightchambers of the heart, or at multiple locations within a single chamberof the heart. There is also a need to develop improved hardware andsoftware for use within implantable devices and within externalprogrammers for recording, tracking and displaying the enhanced codesand markers. It is to these ends that aspects of the invention areprimarily directed.

SUMMARY OF THE INVENTION

[0009] In accordance with a first aspect of the invention, a system isprovided for use in an implantable cardiac stimulation device forgenerating diagnostic information using enhanced event codes. Theenhanced event codes are representative of events detected using aplurality of leads positioned at different locations within the heart,with at least two leads positioned within the atria or with at least twoleads positioned within the ventricles. The system includes means forreceiving signals representative of electrical events detected at therespective locations of the leads, means for generating stimulationsignals using selected leads, and means for generating location-specificevent codes representative of events occurring at the respectivelocations of the leads. The location-specific event codes correspond tothe arrangement of leads and hence include at least two distinct eventcodes associated the atria or at least two distinct event codesassociated with the ventricles. The system also includes means fortransmitting the location-specific event codes to an external programmerfor display thereon.

[0010] In accordance with a second aspect of the invention, an externalprogrammer is provided for use with an implantable cardiac stimulationdevice for displaying diagnostic information received from thestimulation device using enhanced event marker icons. The externalprogrammer includes means for receiving location-specific event codestransmitted from the stimulation device and means for generating graphicdisplays of location-specific event marker icons representative of theevent codes, with a distinct location-specific event marker iconassociated with each distinct location-specific event code. Thelocation-specific event codes provided by the stimulation devicecorrespond to the arrangement of leads of the stimulation device, whichincludes at least two leads in the atria or at least two leads in theventricles.

[0011] By employing the enhanced location-specific event codes and eventmarker icons, the diagnostic information provided by the stimulationdevice and displayed by the external programmer thereby distinguishesevents sensed in the left atrium from events sensed in the right atriumand distinguishes events sensed in the left ventricle from events sensedin the right ventricle. If separate sensing locations are providedwithin each of the four chambers of the heart, the diagnosticinformation distinguishes electrical events occurring in any particularchamber of the heart from all other chambers of the heart. If multiplesensing locations are provided within a particular chamber of the heart,the diagnostic information distinguishes among electrical eventsoccurring at each of the various locations within the chamber.Location-specific event counters may be provided for separately countingevents occurring at the respective locations of the leads so as topermit, for example, display of location-specific event histograms. Thestimulation device and external programmer thereby provide moreeffective tracking of electrical events within the heart and permit moresophisticated displays of diagnostic information.

[0012] In one specific example, wherein the stimulation device haspacing/sensing leads within each of the four chambers of the heart, theexternal programmer displays P_(R) and P_(L) event marker iconsrepresentative of sensed events in the right and left atria,respectively, and R_(R) and R_(L) event marker icons representative ofsensed events in the right and left ventricles, respectively. If thestimulation device is capable of pacing in either the left ventricle,the right ventricle, or both ventricles simultaneously, the externalprogrammer displays V_(L), V_(R), and V_(D) event marker icons,respectively. If the stimulation device is also capable of pacing in theleft and right atria, the external programmer additionally displaysA_(L), A_(R) and A_(D) event marker icons, respectively. For stimulationdevices capable of pacing or sensing at multiple locations within asingle chamber, additional subscripted indices are employed indicatingthe specific location within the chamber. A vertical tick mark isdisplayed by the external programmer adjacent the each event marker iconto indicate the exact time of the corresponding event. If an intrinsicevent sensed in one chamber triggers a stimulation event in anotherchamber, the external programmer displays two vertical tick marksadjacent to one another along with a pair of event marker iconsidentifying the sensed and triggered events. Horizontal lines aredisplayed to indicate the duration of corresponding refractory periods.The event marker icons are displayed adjacent surface ECG signals orIEGM signals, or both. Separate location-specific IEGM signals may bedisplayed, including, for example, a separate IEGM signal per chamber.The external programmer may also be programmed to displaylocation-specific histograms, such as one histogram for right atrialintrinsic events as a function of heart rate and another histogram ofleft atrial intrinsic events as a function of heart rate.

[0013] Other objects and advantages of the invention are achieved aswell. Method embodiments of the invention are also provided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Further features and advantages of the invention may be morereadily understood by reference to the following description taken inconjunction with the accompanying drawings, in which:

[0015]FIG. 1 is illustrates an exemplar display of surface ECG complexesand a set of conventional event markers displayed by an externalprogrammer in accordance with the prior art.

[0016]FIG. 2 is a simplified diagram illustrating an implantablestimulation device in electrical communication with at least threesensing leads implanted into a patient's heart for deliveringmulti-chamber stimulation and shock therapy and for sensing intrinsicheart signals within each of the four chambers of the heart;

[0017]FIG. 3 is a functional block diagram of the implantablestimulation device of FIG. 2 illustrating the basic elements of thestimulation device and also illustrating, in block diagram form, anexternal programmer device for use with the stimulation device;

[0018]FIG. 4 is a block diagram illustrating a portion of a memory ofthe implantable device of FIGS. 2 and 3 for storing enhancedlocation-specific event codes, counters and IEGM signals;

[0019]FIG. 5 is a block diagram of pertinent components of the externalprogrammer of FIG. 3 for use in processing and displaying the eventcodes, counters and IEGM signals received from the device of FIGS. 1 and2;

[0020]FIG. 6 is a block diagram illustrating a portion of a memory ofthe external programmer of FIG. 5 for the storing enhancedlocation-specific event codes, counters and IEGM signals received fromthe stimulation device;

[0021]FIG. 7 is a flow chart illustrating a method performed by thesystem of FIGS. 2-6 for generating, processing, recording, anddisplaying enhanced location-specific diagnostic information thatdistinguishes among the chambers of the heart;

[0022]FIG. 8 is a graph illustrating exemplary ECG complexes along withenhanced event markers that distinguish among the four chambers of theheart as displayed by the external programmer of FIG. 5;

[0023]FIG. 9 is a graph illustrating another exemplary ECG complex asdisplayed by the external programmer of FIG. 5;

[0024]FIG. 10 is a graph illustrating another exemplary ECG complexalong with atrial and ventricular IEGM signals as displayed by theexternal programmer of FIG. 5; and

[0025]FIGS. 11A and 11B are graphs illustrating exemplarylocation-specific histograms as displayed by the external programmer ofFIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

[0026] The following description is of the best mode presentlycontemplated for practicing the invention. This description is not to betaken in a limiting sense but is made merely for the purpose ofdescribing the general principles of the invention. The scope of theinvention should be ascertained with reference to the issued claims. Inthe description of the invention that follows, like numerals orreference designators will be used to refer to like parts or elementsthroughout.

[0027] The description is of a system having an implantable cardiacstimulation device for implantation into a patient and an externalprogrammer for programming the operation of the implantable device andfor processing and displaying diagnostic information received from theimplantable device regarding the condition of the patient and regardingthe condition of the implantable device itself. The diagnosticinformation displayed by the external programmer includes enhancedlocation-specific event marker icons.

[0028] Herein, details of an exemplary implantable device are providedwith reference to FIGS. 2-4, which illustrates a dual-chamberimplantable stimulation device capable of provide cardioversion,defibrillation and pacing stimulation in four chambers of the heart.Then details regarding an exemplary external programmer are providedwith reference to FIGS. 5 and 6. Thereafter, a method performed by theimplantable device and the external programmer to generate and displaythe enhanced diagnostic information is described with reference to FIG.7. Finally, various exemplary graphic displays generated by the externalprogrammer are described with reference to the FIGS. 8-11B.

[0029] Stimulation Device

[0030] As shown in FIG. 2, there is a stimulation device 10 inelectrical communication with a patient's heart 12 by way of threeleads, 20, 24 and 30, suitable for delivering multi-chamber stimulationand shock therapy. To sense atrial cardiac signals and to provide rightatrial chamber stimulation therapy, the stimulation device 10 is coupledto an implantable right atrial lead 20 having at least an atrial tipelectrode 22, which typically is implanted in the patient's right atrialappendage.

[0031] To sense left atrial and ventricular cardiac signals and toprovide left chamber pacing therapy, the stimulation device 10 iscoupled to a “coronary sinus” lead 24 designed for placement in the“coronary sinus region” via the coronary sinus os for positioning adistal electrode adjacent to the left ventricle and/or additionalelectrode(s) adjacent to the left atrium. As used herein, the phrase“coronary sinus region” refers to the vasculature of the left ventricle,including any portion of the coronary sinus, great cardiac vein, leftmarginal vein, left posterior ventricular vein, middle cardiac vein,and/or small cardiac vein or any other cardiac vein accessible by thecoronary sinus.

[0032] Accordingly, an exemplary coronary sinus lead 24 is designed toreceive atrial and ventricular cardiac signals and to deliver leftventricular pacing therapy using at least a left ventricular tipelectrode 26, left atrial pacing therapy using at least a left atrialring electrode 27, and shocking therapy using at least a left atrialcoil electrode 28. For a complete description of a coronary sinus lead,see U.S. patent application Ser. No. 09/457,277, filed Dec. 8, 1999,entitled “A Self-Anchoring, Steerable Coronary Sinus Lead” (Pianca et.al); and U.S. Pat. No. 5,466,254, “Coronary Sinus Lead with AtrialSensing Capability” (Helland), which patents are hereby incorporatedherein by reference.

[0033] The stimulation device 10 is also shown in electricalcommunication with the patient's heart 12 by way of an implantable rightventricular lead 30 having, in this embodiment, a right ventricular tipelectrode 32, a right ventricular ring electrode 34, a right ventricular(RV) coil electrode 36, and an SVC coil electrode 38. Typically, theright ventricular lead 30 is transvenously inserted into the heart 12 soas to place the right ventricular tip electrode 32 in the rightventricular apex so that the RV coil electrode will be positioned in theright ventricle and the SVC coil electrode 38 will be positioned in thesuperior vena cava. Accordingly, the right ventricular lead 30 iscapable of receiving cardiac signals, and delivering stimulation in theform of pacing and shock therapy to the right ventricle.

[0034] As illustrated in FIG. 3, a simplified block diagram is shown ofthe multi-chamber implantable stimulation device 10, which is capable oftreating both fast and slow rhythms with electrical therapy, includingcardioversion, defibrillation, and pacing stimulation. While aparticular multi-chamber device is shown, this is for illustrationpurposes only, and one of skill in the art could readily duplicate,eliminate or disable the appropriate circuitry in any desiredcombination to provide a device capable of treating the appropriatechamber(s) with cardioversion, defibrillation and pacing stimulation.

[0035] The housing 40 for the stimulation device 10, shown schematicallyin FIG. 3, is often referred to as the “can”, “case” or “case electrode”and may be programmably selected to act as the return electrode for all“unipolar” modes. The housing 40 may further be used as a returnelectrode alone or in combination with one or more of the coilelectrodes, 28, 36 and 38, for shocking purposes. The housing 40 furtherincludes a connector (not shown) having a plurality of terminals, 42,44, 46, 48, 52, 54, 56, and 58 (shown schematically and, forconvenience, the names of the electrodes to which they are connected areshown next to the terminals). As such, to achieve right atrial sensingand pacing, the connector includes at least a right atrial tip terminal(A_(R) TIP) 42 adapted for connection to the atrial tip electrode 22.

[0036] To achieve left chamber sensing, pacing and shocking, theconnector includes at least a left ventricular tip terminal (V_(L) TIP)44, a left atrial ring terminal (A_(L) RING) 46, and a left atrialshocking terminal (A_(L) COIL) 48, which are adapted for connection tothe left ventricular ring electrode 26, the left atrial tip electrode27, and the left atrial coil electrode 28, respectively.

[0037] To support right chamber sensing, pacing and shocking, theconnector further includes a right ventricular tip terminal (V_(R) TIP)52, a right ventricular ring terminal (V_(R) RING) 54, a rightventricular shocking terminal (R_(V) COIL) 56, and an SVC shockingterminal (SVC COIL) 58, which are adapted for connection to the rightventricular tip electrode 32, right ventricular ring electrode 34, theRV coil electrode 36, and the SVC coil electrode 38, respectively.

[0038] Thus, with the arrangement of leads of FIG. 2 and terminals ofFIG. 3, the device is capable of separately sensing electrical signalsin each of the four chambers of the heart. Additional leads andterminals may be provided to separately sense electrical signals atmultiple locations within a particular chamber.

[0039] At the core of the stimulation device 10 is a programmablemicrocontroller 60, which controls the various modes of stimulationtherapy. As is well known in the art, the microcontroller 60 typicallyincludes a microprocessor, or equivalent control circuitry, designedspecifically for controlling the delivery of stimulation therapy and mayfurther include RAM or ROM memory, logic and timing circuitry, statemachine circuitry, and I/O circuitry. Typically, the microcontroller 60includes the ability to process or monitor input signals (data) ascontrolled by a program code stored in a designated block of memory. Thedetails of the design and operation of the microcontroller 60 are notcritical to the invention. Rather, any suitable microcontroller 60 maybe used that carries out the functions described herein. The use ofmicroprocessor-based control circuits for performing timing and dataanalysis functions are well known in the art.

[0040] As shown in FIG. 3, an atrial pulse generator 70 and aventricular pulse generator 72 generate pacing stimulation pulses fordelivery by the right atrial lead 20, the right ventricular lead 30,and/or the coronary sinus lead 24 via an electrode configuration switch74. It is understood that in order to provide stimulation therapy ineach of the four chambers of the heart, the atrial and ventricular pulsegenerators, 70 and 72, may include dedicated, independent pulsegenerators, multiplexed pulse generators, or shared pulse generators.The pulse generators, 70 and 72, are controlled by the microcontroller60 via appropriate control signals, 76 and 78, respectively, to triggeror inhibit the stimulation pulses.

[0041] The microcontroller 60 further includes timing control circuitry79 which is used to control the timing of such stimulation pulses (e.g.,pacing rate, atrio-ventricular (AV) delay, atrial interconduction (A-A)delay, or ventricular interconduction (V-V) delay, etc.) as well as tokeep track of the timing of refractory periods, blanking intervals,noise detection windows, evoked response windows, alert intervals,marker channel timing, etc., which is well known in the art.

[0042] The switch 74 includes a plurality of switches for connecting thedesired electrodes to the appropriate I/O circuits, thereby providingcomplete electrode programmability. Accordingly, the switch 74, inresponse to a control signal 80 from the microcontroller 60, determinesthe polarity of the stimulation pulses (e.g., unipolar, bipolar,combipolar, etc.) by selectively closing the appropriate combination ofswitches (not shown) as is known in the art.

[0043] Atrial sensing circuits 82 and ventricular sensing circuits 84may also be selectively coupled to the right atrial lead 20, coronarysinus lead 24, and the right ventricular lead 30, through the switch 74for detecting the presence of cardiac activity in each of the fourchambers of the heart. Accordingly, the atrial (ATR. SENSE) andventricular (VTR. SENSE) sensing circuits, 82 and 84, may includededicated sense amplifiers, multiplexed amplifiers, or sharedamplifiers. The switch 74 determines the “sensing polarity” of thecardiac signal by selectively closing the appropriate switches, as isalso known in the art. In this way, the clinician may program thesensing polarity independent of the stimulation polarity.

[0044] Each sensing circuit, 82 and 84, preferably employs one or morelow power, precision amplifiers with programmable gain and/or automaticgain control, bandpass filtering, and a threshold detection circuit, asknown in the art, to selectively sense the cardiac signal of interest.The automatic gain control enables the device 10 to deal effectivelywith the difficult problem of sensing the low amplitude signalcharacteristics of atrial or ventricular fibrillation. The outputs ofthe atrial and ventricular sensing circuits, 82 and 84, are connected tothe microcontroller 60 which, in turn, are able to trigger or inhibitthe atrial and ventricular pulse generators, 70 and 72, respectively, ina demand fashion in response to the absence or presence of cardiacactivity in the appropriate chambers of the heart. For arrhythmiadetection, the device 10 utilizes the atrial and ventricular sensingcircuits, 82 and 84, to sense cardiac signals to determine whether arhythm is physiologic or pathologic. As used herein “sensing” isreserved for the noting of an electrical signal, and “detection” is theprocessing of these sensed signals and noting the presence of anarrhythmia. The timing intervals between sensed events are thenclassified by the microcontroller 60 by comparing them to a predefinedrate zone limit (i.e., bradycardia, normal, low rate VT, high rate VT,and fibrillation rate zones) and various other characteristics (e.g.,sudden onset, stability, physiologic sensors, and morphology, etc.) inorder to determine the type of remedial therapy that is needed (e.g.,bradycardia pacing, anti-tachycardia pacing, cardioversion shocks ordefibrillation shocks, collectively referred to as “tiered therapy”).

[0045] Cardiac signals are also applied to the inputs of ananalog-to-digital (AD) data acquisition system 90. The data acquisitionsystem 90 is configured to acquire intracardiac electrogram signals,convert the raw analog data into a digital signal, and store the digitalsignals for later processing and/or telemetric transmission to anexternal device 102. The data acquisition system 90 is coupled to theright atrial lead 20, the coronary sinus lead 24, and the rightventricular lead 30 through the switch 74 to sample cardiac signalsacross any pair of desired electrodes.

[0046] The microcontroller 60 is further coupled to a memory 94 by asuitable data/address bus 96, wherein the programmable operatingparameters used by the microcontroller 60 are stored and modified, asrequired, in order to customize the operation of the stimulation device10 to suit the needs of a particular patient. Such operating parametersdefine, for example, pacing pulse amplitude, pulse duration, electrodepolarity, rate, sensitivity, automatic features, arrhythmia detectioncriteria, and the amplitude, waveshape and vector of each shocking pulseto be delivered to the patient's heart 12 within each respective tier oftherapy. A feature of the invention is the ability to sense and store arelatively large amount of data (e.g., from the data acquisition system90), which data may then be used for subsequent analysis to guide theprogramming of the device. In particular, the memory storeslocation-specific data such as location-specific event records and IEGMdata. In a primary example described herein, the memory separatelystores diagnostic data for each of the four chambers of the heart. Aportion of memory 94 is shown in FIG. 4. As can be seen the memorystores location-specific event records, counter data and IEGM data foreach of the four chambers of the heart. As will be described furtherbelow, the location-specific data is ultimately transmitted to anexternal programmer for display thereon. Processing of thelocation-specific data, including generation of the location-specificevent records and the storage thereof in the memory, is controlled by alocation-specific event processing unit 95 of the microcontroller. Thelocation-specific event processing unit maybe a software module of acontrol program executed by the controller.

[0047] Advantageously, the operating parameters of the implantabledevice 10 may be non-invasively programmed into the memory 94 through atelemetry circuit 100 in telemetric communication with the externaldevice 102, such as a programmer, transtelephonic transceiver, or adiagnostic system analyzer. The telemetry circuit 100 is activated bythe microcontroller by a control signal 106. The telemetry circuit 100advantageously allows intracardiac electrograms and status informationrelating to the operation of the device 10 (as contained in themicrocontroller 60 or memory 94) to be sent to the external device 102through an established communication link 104. For examples of suchdevices, see U.S. Pat. No. 4,809,697, entitled “Interactive Programmingand Diagnostic System for use with Implantable Pacemaker” (Causey, IIIet al.); U.S. Pat. No. 4,944,299, entitled “High Speed Digital TelemetrySystem for Implantable Device” (Silvian); and U.S. patent applicationSer. No. 09/223,42:2, filed Dec. 30, 1998, entitled “EfficientGeneration of Sensing Signals in an Implantable Medical Device such as aPacemaker or ICD” (note: this relates to transfer of EGM data) (McClureet al.), which patents are hereby incorporated herein by reference.

[0048] In the preferred embodiment, the stimulation device 10 furtherincludes a physiologic sensor 108, commonly referred to as a“rate-responsive” sensor because it is typically used to adjust pacingstimulation rate according to the exercise state of the patient.However, the physiological sensor 108 may further be used to detectchanges in cardiac output, changes in the physiological condition of theheart, or diurnal changes in activity (e.g., detecting sleep and wakestates). Accordingly, the microcontroller 60 responds by adjusting thevarious pacing parameters (such as rate, AV Delay, V-V Delay, etc.) atwhich the atrial and ventricular pulse generators, 70 and 72, generatestimulation pulses.

[0049] The stimulation device additionally includes a battery 110 thatprovides operating power to all of the circuits shown in FIG. 3. For thestimulation device 10, which employs shocking therapy, the battery 110must be capable of operating at low current drains for long periods oftime, and then be capable of providing high-current pulses (forcapacitor charging) when the patient requires a shock pulse. The battery110 must also have a predictable discharge characteristic so thatelective replacement time can be detected. Accordingly, the device 10preferably employs lithium/silver vanadium oxide batteries or lithiumiodine cells.

[0050] The stimulation device 10 further includes a magnet detectioncircuitry (not shown), coupled to the microcontroller 60. It is thepurpose of the magnet detection circuitry to detect when a magnet isplaced over the stimulation device 10, which magnet may be used by aclinician to perform various test functions of the stimulation device 10and/or to signal the microcontroller 60 that the external programmer 102is in place to receive or transmit data to the microcontroller 60through the telemetry circuits 100.

[0051] As further shown in FIG. 3, the device 10 is shown as having animpedance measuring circuit 112 which is enabled by the microcontroller60 via a control signal 114. The impedance measuring circuit 112 is notcritical to the invention and is shown for only completeness.

[0052] In the case where the stimulation device 10 is intended tooperate as an implantable cardioverter/defibrillator (ICD) device, itmust detect the occurrence of an arrhythmia, and automatically apply anappropriate electrical shock therapy to the heart aimed at terminatingthe detected arrhythmia. To this end, the microcontroller 60 furthercontrols a shocking circuit 116 by way of a control signal 118. Theshocking circuit 116 generates shocking pulses of low (up to 0.5Joules), moderate (0.5-10 Joules), or high energy (11 to 40 Joules), ascontrolled by the microcontroller 60. Such shocking pulses are appliedto the patient's heart 12 through at least two shocking electrodes, andas shown in this embodiment, selected from the left atrial coilelectrode 28, the RV coil electrode 36, and/or the SVC coil electrode38. As noted above, the housing 40 may act as an active electrode incombination with the RV electrode 36, or as part of a split electricalvector using the SVC coil electrode 38 or the left atrial coil electrode28 (i.e., using the RV electrode as a common electrode).

[0053] Cardioversion shocks are generally considered to be of low tomoderate energy level (so as to minimize pain felt by the patient),and/or synchronized with an R-wave and/or pertaining to the treatment oftachycardia. Defibrillation shocks are generally of moderate to highenergy level (i.e., corresponding to thresholds in the range of 5-40Joules), delivered asychronously (since R-waves may be toodisorganized), and pertaining exclusively to the treatment offibrillation. Accordingly, the microcontroller 60 is capable ofcontrolling the synchronous or asynchronous delivery of the shockingpulses.

[0054] External Programmer

[0055]FIG. 4 illustrates pertinent components of an external programmerfor use in programming an implantable cardiac stimulation device such asthe device of FIGS. 2 and 3. Briefly, the programmer permits a physicianor other user to program the operation of the implanted device and toretrieve and display information received from the implanted device suchas IEGM data and device diagnostic data. In particular, the programmeris provided with internal components capable of separately receiving,storing and processing event markers representative of events paced orsensed in any of the four chambers of the heart. Additionally, theexternal programmer receives and displays ECG data from separateexternal ECG leads that may be attached to the patient. Depending uponthe specific programming of the external programmer, programmer 200 mayalso be capable of processing and analyzing data received from theimplanted device and from the ECG leads to, for example, renderpreliminary diagnosis as to medical conditions of the patient or to theoperations of the implanted device.

[0056] Now, considering the components of programmer 200, operations ofthe programmer are controlled by a CPU 202, which may be a generallyprogrammable microprocessor or microcontroller or may be a dedicatedprocessing device such as an application specific integrated circuit(ASIC) or the like. Software instructions to be performed by the CPU areaccessed via an internal bus 204 from a read only memory (ROM) 206.Additional software may be accessed from a hard drive 208, floppy drive210, and CD ROM drive 212, or other suitable permanent mass storagedevice. Depending upon the specific implementation, a basic input outputsystem (BIOS) is retrieved from the ROM by CPU at power up. Based uponinstructions provided in the BIOS, the CPU “boots up” the overall systemin accordance with well-established computer processing techniques.

[0057] Once operating, the CPU displays a menu of programming options tothe user via an LCD display 214 or other suitable computer displaydevice. To this end, the CPU may, for example, display a menu ofspecific programming parameters of the implanted device to be programmedor may display a menu of types of diagnostic data to be retrieved anddisplayed. In response thereto, the physician enters various commandsvia either a touch screen 216 overlaid on the LCD display or through astandard keyboard 218 supplemented by additional custom keys 220, suchas an EVVI key.

[0058] Typically, the physician initially controls the programmer 200 toretrieve data stored within the implanted cardiac stimulation device andto also retrieve ECG data from ECG leads, if any, coupled to thepatient. To this end, CPU 202 transmits appropriate signals to atelemetry subsystem 222, which provides components for directlyinterfacing with the implanted device, and the ECG leads. Telemetrysubsystem 222 includes its own separate CPU 224 for coordinating theoperations of the telemetry subsystem. Main CPU 202 of programmercommunicates with telemetry subsystem CPU 224 via the internal bus.Telemetry subsystem additionally includes a telemetry circuit 226connected to a telemetry wand 228, which, in turn, receives andtransmits signals electromagnetically from a telemetry unit of theimplanted device. The telemetry wand is placed over the chest of thepatient in the vicinity of the implanted device to permit reliabletransmission of data between the telemetry wand and the implanteddevice. Typically, at the beginning of the programming session, theexternal programming device controls the implanted device viaappropriate signals generated by the telemetry wand to output allpreviously recorded patient and device diagnostic information. Patientdiagnostic information includes, for example, recorded IEGM data andstatistical patient data such as the percentage of paced versus sensedheartbeats. Device diagnostic data includes, for example, informationrepresentative of the operation of the implanted device such as leadimpedances, battery voltages, battery recommended replacement time (RRT)information and the like. Preferably, all data stored within theimplanted device is recorded within “event records” which facilitate theefficient storage and transmission of the data. Additional informationpertaining to the recording, transmission, and processing of eventrecord information may be found within the aforementioned U.S. patent toSnell. Unlike the system of Snell, however, the data provided by thestimulation device and the event markers displayed by the externalprogrammer distinguish among a greater number of sensing locations, suchas between the left and right chambers of the heart or among multiplelocations within a single chamber of the heart. In the primary exampledescribed herein, the memory of the external programmer stores thelocation-specific event records, counter data and IEGM data for each ofthe four chambers of the heart received from the stimulation device. Aportion of ROM 206 is shown in FIG. 6. As can be seen, the ROM storeslocation-specific event records, counter data and IEGM data for each ofthe four chambers of the heart. A location-specific event marker displaygeneration unit within the CPU controls the generation of graphicdisplays of diagnostic information based on the location-specific eventrecords, counter data and IEGM data stored in RM 206. Thelocation-specific event processing unit maybe a software module of acontrol program executed by the CPU.

[0059] Data retrieved from the implanted device is stored by externalprogrammer 200 either within a random access memory (RAM) 230, harddrive 208 or within a floppy diskette placed within floppy drive 210.Additionally, or in the alternative, data may be permanently orsemi-permanently stored within a compact disk (CD) or other digitalmedia disk, if the overall system is configured with a drive forrecording data onto digital media disks, such as a write once read many(WORM) drive.

[0060] Once all patient and device diagnostic data previously storedwithin the implanted device is transferred to programmer 200, theimplanted device may be further controlled to transmit additional datain real time as it is detected by the implanted device, such asadditional IEGM data, lead impedance data, and the like. Additionally,or in the alternative, telemetry subsystem 222 receives ECG signals fromECG leads 232 via an ECG processing circuit 234. As with data retrievedfrom the implanted device itself, signals received from the ECG leadsare stored within one or more of the storage devices of the externalprogrammer. Typically, ECG leads output analog electrical signalsrepresentative of the ECG. Accordingly, ECG circuit 234 includes analogto digital conversion circuitry for converting the signals to digitaldata appropriate for further processing within programmer. Dependingupon the implementation, the ECG circuit may be configured to convertthe analog signals into event record data for ease of processing alongwith the event record data retrieved from the implanted device.Typically, signals received from the ECG leads are received andprocessed in real time.

[0061] Thus the programmer receives data both from the implanted deviceand from the external ECG leads. Data retrieved from the implanteddevice includes parameters representative of the current programmingstate of the implanted device. Under the control of the physician, theexternal programmer displays the current programming parameters andpermits the physician to reprogram the parameters. To this end, thephysician enters appropriate commands via any of the aforementionedinput devices and, under control of CPU 202, the programming commandsare converted to specific programming parameters for transmission to theimplanted device via telemetry wand 228 to thereby reprogram theimplanted device. Techniques for programming an implanted cardiacstimulation device may be found in U.S. Pat. No. 5,716,382 entitled“Programmer For An Implantable Cardiac Stimulating Device”. Prior toreprogramming specific parameters, the physician may control theexternal programmer to display any or all of the data retrieved from theimplanted device or from the ECG leads, including displays of ECGs,IEGMs, and statistical patient information. In particular, the externalprogrammer can be controlled to generate graphic displays or printoutsof location-specific; IEGMs and event markers. Depending upon theprogramming of the external programmer and the commands entered, theprogrammer may display either a single combined IEGM representative of acombination of the IEGM signals from the four chambers of the heart ormay display the individual IEGM signals separately. Further informationpertaining to information that may be displayed using the programmer maybe found in U.S. Pat. No. 5,974,341 entitled “Method And Apparatus ForDetecting And Displaying Diagnostic Information In Conjunction WithIntracardiac Electrograms And Surface Electrocardiograms”. Any or all ofthe information displayed by programmer may also be printed using aprinter 236.

[0062] Programmer 200 also includes a modem 238 to permit directtransmission of data to other programmers via the public switchedtelephone network (PSTN) or other interconnection line, such as a T1line or fiber optic cable. Depending upon the implementation, the modemmay be connected directly to internal bus 204 may be connected to theinternal bus via either a serial port 240 or a parallel port 242. Otherperipheral devices may be connected to the external programmer viaserial port 240 or a parallel port 242 as well. Although one of each isshown, a plurality of input output (IO) ports may be provided. A speaker244 is included for providing audible tones to the user, such as awarning beep in the event the physician provides improper input.Telemetry subsystem 222 additionally includes an analog output circuit246 for controlling the transmission of analog output signals.

[0063] With the programmer configured as shown, a physician or otheruser operating the external programmer is capable of retrieving,processing and displaying a wide range of information received from theECG leads or from the implanted device and to reprogram the implanteddevice if needed. The descriptions provided herein with respect to FIG.4 are intended merely to provide an overview of the operation ofprogrammer and are not intended to describe in detail each and everyfeature of the hardware and software of the device and is not intendedto provide an exhaustive list of the functions performed by the device.

[0064] Processing of Location-specific Diagnostic Data

[0065]FIG. 7 is a flow chart illustrating the operation of theprogrammer and implantable device to permit the physician to generateprintouts and displays of location-specific diagnostic data such asIEGMs and event markers. In the flow chart, the various steps of themethod are summarized in individual “blocks”. Such blocks describespecific actions or decisions that are made or carried out as the methodproceeds. Where a microcontroller (or equivalent) is employed, the flowcharts presented herein provide the basis for a “control program” thatmay be used by such a microcontroller (or equivalent) to effectuate thedesired control of the stimulation device. Those skilled in the art mayreadily write such a control program based on the flow charts and otherdescriptions presented herein. Steps performed by the implanted deviceare shown on the left. Steps performed by the external programmer areshown on the right.

[0066] Briefly, the implanted device operates to record IEGM signals andto detect, record and count location-specific events whiledistinguishing among the various chambers of the heart. The stimulationdevice transmits the data to the external programmer, which operates todisplay event marker icons identifying the location-specific eventsalong with the IEGM signals received from the stimulation device oralong with separately detected surface ECG signals. The externalprogrammer also operates to display the counts of the location-specificevents in the form of histograms or other graphical displays.

[0067] Initially, at step 300, the implantable stimulation device inputsseparate location-specific IEGM signals from each of the four chambersof the heart via the aforementioned sensing leads. Hence, at step 300,the stimulation device receives separate left and right atrial IEGMsignals and separate left and right ventricular IEGM signals. At step302 the location-specific IEGM signals are stored within an internalmemory of the stimulation device (memory 94 of FIG. 3). As the signalsare received, the stimulation device analyzes the location-specific IEGMsignals to detect and record intrinsic deflection events found therein,at step 304. The intrinsic events detected within the right and leftatria and right and left ventricles are internally designated andrecorded using event codes identifying the specific chamber. Othersensed information may also be detected and recorded such as the lengthsof refractory periods and the like. Each intrinsic event, as it isrecorded, is also time stamped to indicate the date and time of theevent. Depending upon the intrinsic events detected within the IEGMsignals and on the programming of the implanted stimulation device, thestimulation device delivers therapy at step 306 usually in the form ofindividual pacing pulses delivered to one or more of the chambers of theheart. The stimulation device also records the stimulation events atstep 306 in the memory along with the detected intrinsic events.Stimulation administered to the right and left atria and right and leftventricles is internally designated and recorded using event codesidentifying the specific chamber. Stimulation administered to multiplechambers simultaneously is internally designated and recorded using aappropriate multi-chamber event codes. Depending upon its programmingand capabilities, the stimulation device also may be capable of sensingin one chamber and delivering a responsive pacing pulse in anotherchamber. This is desirable if, for example, an intrinsic pacing event isdetected in only the left ventricle rather than within both the left andright ventricles. If the stimulation device is capable of sensing in onechamber, then pacing in another, or vice versa, the two events arestored separately along with a code indicating that the two events arerelated. As will be described below, the programmer detects relatedevents and generates a unique display. Each stimulation event, as it isrecorded, is also time stamped to indicate the date and time of theevent. Preferably, the intrinsic events and stimulation events arerecorded using the event record format of the aforementioned Snellpatent, modified as needed to accommodate the various location-specificevent codes. The actual event codes may be any suitable alphanumericalcodes or other codes suitable for distinguishing the events for storagewithin the memory. They may, for example, be unique sequences of binarynumbers.

[0068] Also as events are recorded, various internal counters maintainedby the stimulation device are updated, at step 308, to track the variousevents. For example, separate location-specific intrinsic event countersare incremented whenever an intrinsic event is detected within one ormore of the separate IEGM signals. The counters may have separate binsor registers for different heart rate ranges to permit location-specifichistograms of intrinsic events to be recorded as a function of heartrate. Other counters may be provided for separately tracking events thatare not location-specific, such stimulation events occurring in bothleft and right chambers. For example, for stimulation pulses applied toboth ventricles, a dual chamber ventricular stimulation counter isupdated. In other cases, although events may be separately detected indifferent chambers, a single counter may be used to count the sum totalof all events in the separate chambers. For example, a counter may beprovided to count all intrinsic events in the atria, withoutdistinguishing between the left and right atria. Other counters may beprovided to tracking coupling intervals between successive complexesbased on whether a premature beat or an intrinsic beat arises from theleft or right atria or left or right ventricle. As can be appreciated, awide variety of counters may be employed for tracking a wide variety ofinformation. No attempt is made herein to enumerate or describe the manycounters that may be employed. In general, any conventionalnon-location-specific counter can be modified, in accordance with theprinciples of the invention, to separately count location-specific data.

[0069] Steps 300-308 are continuously performed while the stimulationdevice is operating within the patient to process newly receivedlocation-specific IEGM signals from the various chambers of the heartand to store location-specific event records and to updatelocation-specific counters. Preferably, sufficient internal memory isprovided to store the location-specific IEGM signals and event recordsover a relatively long period of time to permit subsequent transmissionto the external programmer. If the event record memory or the IEGMmemory becomes full, the earliest recorded IEGM signals and eventrecords are preferably overwritten by newly detected IEGM signals andevent records.

[0070] Subsequently, perhaps during a follow-up session with thephysician, the implantable stimulation device is controlled at step 310to transmit the location-specific event records, IEGM data, and countervalues and any other diagnostic information to the external programmer.The programmer may request that all previously recorded event recordsand IEGM data be transferred to the programmer or that only eventrecords and IEGM data associated with specific periods of time betransmitted. Alternatively, the programmer may request that onlyreal-time IEGM data and event records be transmitted such that thephysician may generate displays of current conditions within the heartof the patient and within the implantable device.

[0071] The programmer at step 312 receives and stores the transmitteddata. At step 314, the programmer receives surface ECG data, ifavailable, and at step 316 generates corresponding graphic displays orprintouts of the location-specific event records and IEGM data and thesurface ECG signals. To this end, for each event recorded in the eventrecord data, event markers are generated and displayed using icons thatdistinguish among the different types of events and among the fourchambers of the heart. For example, L and R subscripts may be employedto distinguish between left and right chambers of the heart. A Dsubscript may be employed to represent a dual chamber event. In onespecific example, the following icons are used to represent intrinsicevents detected in the right and left atria and right and leftventricles respectively: P_(R), P_(L), R_(R), and R_(L). Also in theexample, the following icons are used to represent stimulation eventsapplied to the right and left atria and right and left ventriclesrespectively: A_(R), A_(L), V_(R), and V_(L). Dual chamber pacing in theatria is represented by A_(D) whereas dual chamber pacing in theventricles is represented by V_(D).

[0072] As can be appreciated, numerous other representation systems maybe employed. The various event markers and icons described above aremerely exemplary. For example, rather than providing R_(L) to identifyan intrinsic event detected in the left ventricle, the system may employa V_(SL). Likewise, rather than using a P_(R) to identify an intrinsicevent sensed in the right atrium, the system may instead employ a A_(SR)to identify the same event. If two or more pacing or sensing sites arelocated within a single chamber of the heart, numerical indices may beemployed to distinguish there-between. For example, an intrinsic eventdetected at a first sensing location within the left atrium may beidentified using the event marker P_(L1) whereas an intrinsic eventdetected at a second location within the left atrium may be identifiedusing the event marker P_(L2). Depending upon the programming of thesystem, and the display capabilities of the programmer, different colorsmay be employed to distinguish different event marker icons.

[0073] Preferably, the event marker icons are displayed along sideeither the IEGM data, the ECG data or both. Any other data provided bythe stimulation device is displayed numerically or graphically dependingupon the nature of the data and the preferences of the physician. Forexample, refractory periods are displayed using horizontal bars. Insofaras the IEGM data is concerned, because the programmer receives fourseparate IEGM data streams corresponding to the four chambers of theheart, there is considerable flexibility as to the generation of IEGMgraphic displays. Under the control of the physician, the programmer maydisplay, for example, a single IEGM signal that represents a combinationof the four separate IEGM channels. In this regard, appropriatefiltering or averaging software may be employed to combine the four IEGMchannels into a single IEGM signal. Alternatively, the physician maywish to display IEGM signals wherein left and right chambers areaveraged together, but wherein separate displays are presented for theatrial and ventricular signals. In still other cases, the physician maywish to display all four individual IEGM signals. As can be appreciated,wide ranges of choices are available to the physician. In each case,event markers are preferably displayed alongside the IEGM signals toindicate the relative timing relationship of the events and the portionsof the IEGM signals displayed.

[0074]FIG. 8 is an exemplary display of enhanced event markers incombination with the same ECG complexes of FIG. 1 (now denoted 332, 334and 336). Unlike the conventional event markers of FIG. 1, the eventmarkers of FIG. 8 properly show that the events of complexes 332 and 336were detected within the right chambers of the heart and the events ofcomplex 334 were detected within the left chambers. A short verticaltick mark is displayed precisely indicating the point in time thecorresponding event was detected. FIG. 8 also illustrates the use ofhorizontal lines or bars to indicate the length of refractory periodsassociated with the P-waves and R-waves.

[0075] As noted above, the implanted device may be programmed to delivera stimulation pulse to the right ventricle if an intrinsic pacing eventis detected only in the left ventricle, or vice versa. If this is thecase, the device thereby stores related event markers. Upon detecting apair of related event markers, the programmer displays both eventmarkers along with the ECG complex and employs two short vertical tickmarks to indicate the related sensed/paced events. An example isillustrated in FIG. 9. As can be seen, two short vertical tick marks aredisplayed along with adjacent RR and VL event marker icons indicatingthat an intrinsic event was detected in the right ventricle and astimulation pulse was generated in the left ventricle.

[0076]FIG. 10 illustrates a combination display of both atrial andventricular IEGM signals and a surface ECG complex 337 along withlocation-specific event marker icons. The figure specificallyillustrates an intrinsic atrial deflection point 338 used by theimplanted device to detect the intrinsic atrial event and an intrinsicventricular deflection point 340 used by the implanted device to detectthe intrinsic ventricular event. In the example of FIG. 10, only asingle atrial IEGM signal is illustrated and only a single ventricularIEGM signal is illustrated. In other embodiments, separate left andright atrial and left and right ventricular IEGM signals are displayedby the external programmer.

[0077] Returning again to the flow chart of FIG. 7, at step 318 theprogrammer generates graphic displays or printouts of thelocation-specific counter values such as location-specific histogramsand the like. FIGS. 11A and 11B illustrates a pair of location-specifichistograms illustrating counts of intrinsic events detected in the leftand right atria as a function of heart rate. Other location-specifichistograms may be displayed as well such as histograms illustratingcounts of intrinsic events detected in the left and right ventricles asa function of heart rate or histograms illustrating counts ofstimulation events in the various chambers of the heart.

[0078] What has been described are systems for generating, storing,processing and graphically displaying a wide variety of informationpertaining to events detected by an implantable cardiac stimulationdevice. The various functional components of the exemplary system may beimplemented using any appropriate technology including, for example,microprocessors running software programs or application specificintegrated circuits (ASICs) executing hard-wired logic operations.Although described with respect to a pacemaker used in conjunction withan external programmer, aspects of the invention are applicable to othersystems, such as systems employing other implantable cardiac stimulationdevices or systems employing other types of external interfaces for usewith the implantable device. The exemplary embodiments of the inventiondescribed herein are merely illustrative of the invention and should notbe construed as limiting the scope of the invention.

What is claimed is:
 1. In an implantable cardiac stimulation device forimplant into a patient wherein the stimulation device has a plurality ofleads positioned at different locations within the heart of the patientwith at least two leads positioned within the atria or with at least twoleads positioned within the ventricles, a system for comprising: meansfor receiving signals representative of electrical events detected atthe respective locations of the leads; means for generating stimulationsignals using selected leads; means for generating location-specificevent codes representative of events occurring at the respectivelocations of the leads, with at least two distinct location-specificevent codes being associated the atria or with at least two distinctlocation-specific event codes being associated with the ventricles; andmeans for transmitting the location-specific event codes to an externalprogrammer.
 2. The system of claim 1 wherein at least two leads arepositioned in the atria and wherein the means for generatinglocation-specific event codes generates codes that distinguish betweenthe left and right atria.
 3. The system of claim 1 wherein at least twoleads are positioned in the ventricles and wherein the means forgenerating location-specific event codes generates codes thatdistinguish between the left and right ventricles.
 4. The system ofclaim 1 wherein at least one lead is positioned in each chamber of theheart and wherein the means for generating location-specific event codesgenerates codes that distinguish among the four chambers of the heart.5. The system of claim 1 wherein the means for generating stimulationsignals generates dual chamber stimulation signals using at least twoleads in separate chambers of the heart and wherein the means forgenerating event codes also generates event codes representative of thedual chamber stimulation signals.
 6. The system of claim 1 wherein themeans for receiving signals and the means for generating a stimulationsignals operate to detect an intrinsic electrical event in one chamberof the heart and immediately generate a stimulation signal for deliveryto another chamber of the heart.
 7. The system of claim 6 wherein themeans for generating location-specific event codes generates linkedevent codes for the intrinsic event detected in one chamber and thestimulation signal generated for delivery to the other chamber of theheart.
 8. The system of claim 1 further including means for recordingthe location-specific event codes.
 9. The system of claim 1 furtherincluding location-specific means for separately counting eventsoccurring at the respective locations of the leads.
 10. The system ofclaim 1 further including means for determining a heart rate of thepatient and wherein the location-specific means for counting eventsseparately counts events at different heart rates so as to generate alocation-specific histogram of events as a function of heart rate. 11.The system of claim 1 further including means for detecting refractoryperiods associated with electrical events.
 12. The system of claim 1further including means for generating location-specific intracardiacelectrograms (IEGMs).
 13. An external programmer for receiving anddisplaying information transmitted from the implantable cardiacstimulation device of claim
 1. 14. The external programmer of claim 13comprising: means for receiving location-specific event codestransmitted from the implantable cardiac stimulation device; and meansfor generating graphic displays of location-specific event marker iconsrepresentative of the event codes, with the location-specific eventmarker icons being representative of the locations of the respectiveleads at which the events associated with the event codes occurred. 15.The system of claim 14 further including means for receiving surfaceelectrocardiograms (ECGs) and wherein the means for generating graphicdisplays also generates graphic displays of the surface ECGs.
 16. In animplantable cardiac stimulation device for implant into a patientwherein the stimulation device has a plurality of leads positioned atdifferent locations within the heart of the patient with at least twoleads positioned within the atria or with at least two leads positionedwithin the ventricles, a system for processing signals received from theleads comprising: a set of sensors operative to receive signals from theleads representative of electrical events detected at the respectivelocations of the leads; a set of pulse generators operative to generatestimulation pulses for delivery to the heart using selected leads; alocation-specific data processing unit operative to generatelocation-specific event codes representative of events occurring at theleads, with at least two distinct location-specific event codes beingassociated the atria or with at least two distinct location-specificevent codes being associated with the ventricles; and a telemetrycircuit operative to transmit the location-specific event codes to anexternal programmer device.
 17. The system of claim 16 wherein at leasttwo leads are positioned in the atria and wherein the location-specificdata processing unit generates codes that distinguish between the leftand right atria.
 18. The system of claim 16 wherein at least two leadsare positioned in the ventricles and wherein the location-specific dataprocessing unit generates codes that distinguish between the left andright ventricles.
 19. The system of claim 16 wherein at least one leadis positioned in each chamber of the heart and wherein thelocation-specific data processing unit generates codes that distinguishamong the four chambers of the heart.
 20. The system of claim 16 whereinthe set of pulse generators generates dual chamber stimulation pulsesusing at least two leads in separate chambers of the heart and whereinthe means for generating event codes also generates event codesrepresentative of the dual chamber stimulation signals, and with thedual chamber event codes being distinct from single chamber event codes.21. The system of claim 16 wherein the location-specific data processingunit links event codes for related events, including events detected inone chamber which trigger generation of a stimulation pulse in anotherchamber.
 22. The system of claim 16 further including a memory operativeto record the location-specific event codes.
 23. The system of claim 16wherein the location-specific data processing unit includeslocation-specific counters for counting events occurring at therespective locations of the leads, with the counters separately countingevents occurring at different lead locations.
 24. The system of claim 23further including a heart rate determination unit operative to determinethe heart rate of the patient and wherein the location-specific countersseparately count events at different heart rates so as to generatelocation-specific histograms of events as a function of heart rate. 25.The system of claim 16 further including a heart rate determination unitoperative to detect refractory periods associated with the events. 26.An external programmer for receiving and displaying informationtransmitted from the implantable cardiac stimulation device of claim 16.27. The external programmer of claim 26 comprising: a telemetrysubsystem means operative to receive the location-specific event codestransmitted from the implantable cardiac stimulation device; and aprocessor operative to generate graphic displays of location-specificevent marker icons representative of the location-specific event codes,with the event marker icons being representative of the locations of therespective leads at which the events associated with the event codesoccurred.
 28. In an implantable cardiac stimulation device for implantinto a patient, the stimulation device having a controller, a telemetryunit, and a set of sensors and pulse generators connected to a pluralityof leads positioned at different locations within the heart of thepatient, with at least two leads positioned within the atria or with atleast two leads positioned within the ventricles, a method forcomprising the steps of: receiving sensor signals from the sensorsrepresentative of electrical events detected at the respective locationsof the leads; generating stimulation pulses using the pulse generatorsfor delivery to the heart using selected leads; generatinglocation-specific event codes using the controller, the event codesbeing based on the sensor signals and stimulation pulses, with at leasttwo distinct location-specific event codes being associated the atria orwith at least two distinct location-specific event codes beingassociated with the ventricles; and transmitting the location-specificevent codes to an external programmer using the telemetry unit.
 29. Themethod of claim 28 further including the steps of: generating dualchamber stimulation signals using the pulse generators for delivery toat least two leads in separate chambers of the heart; and generatingdual chamber event codes using the controller, the dual chamber eventcodes being representative of the dual chamber stimulation signals. 30.The method of claim 28 wherein the step of generating location-specificevent codes includes the step of linking event codes for related events,including events detected in one chamber which trigger generation of astimulation signal in another chamber.
 31. The method of claim 30further including the step of recording the location-specific eventcodes.
 32. The method of claim 28 further including the step of countingevents occurring at the respective locations of the leads whiledistinguishing among events occurring at different leads.
 33. The methodof claim 28 further including the step of: determining a heart rate ofthe patient and wherein the step of counting events is performed toseparately count events at different heart rates so as to generate alocation-specific histogram of events as a function of heart rate. 34.The method of claim 28 further including the step of: detectingrefractory periods associated with the events.
 35. The method of claim28 further including the steps, performed by an external programmer, of:receiving location-specific event codes transmitted from the implantablecardiac stimulation device; and graphically displaying location-specificevent marker icons representative of the event codes, with thelocation-specific event marker icons being representative of thelocations of the respective leads at which the events associated withthe event codes occurred.
 36. In an implantable cardiac stimulationdevice for implant into a patient wherein the stimulation device has aplurality of leads positioned at different locations within the heart ofthe patient with at least one lead positioned within each chamber of theheart, a system comprising: means for receiving signals representativeof electrical events detected at the respective locations of the leads;means for generating location-specific intracardiac electrograms (IEGMS)based on the signals received from the leads; means for generatingstimulation signals using selected leads; means for generatinglocation-specific event codes representative of events occurring at therespective locations of the leads, with at least one distinctlocation-specific event code being associated with each chamber of theheart; means for recording the location-specific event codes and IEGMs;and means for transmitting the location-specific event codes and IEGMsto an external programmer.
 37. An implantable cardiac stimulation deviceand external programmer system comprising: an implantable cardiacstimulation device for implant into a patient wherein the stimulationdevice has a plurality of leads positioned at different locations withinthe heart of the patient with at least one lead within each chamber ofthe heart; the stimulation device having a set of sensors operative toreceive signals from the leads representative of electrical eventsdetected at the respective locations of the leads, a set of pulsegenerators operative to generate stimulation pulses for delivery to theheart using selected leads, a location-specific data processing unitoperative to generate location-specific event codes representative ofevents occurring at the leads, with at least one distinctlocation-specific event code being associated with each chamber of theheart, and a telemetry circuit; and an external programmer for receivingand displaying information transmitted from the implantable cardiacstimulation; with the external programmer having a telemetry subsystemmeans operative to receive the location-specific event codes transmittedfrom the implantable cardiac stimulation device and a processoroperative to generate graphic displays of location-specific event markericons representative of the location-specific event codes, with theevent marker icons being representative of the locations of therespective leads at which the events associated with the event codesoccurred.
 38. In an implantable cardiac stimulation device for implantinto a patient, the stimulation device having a controller, a telemetryunit, and a set of sensors and pulse generators connected to a pluralityof leads positioned at different locations within the heart of thepatient, with at least one lead within each chamber of the heart, amethod for comprising the steps of: receiving signals representative ofelectrical events detected at the respective locations of the leads;generating location-specific intracardiac electrograms (IEGMs) based onthe signals received from the leads; generating stimulation signalsusing selected leads; generating location-specific event codesrepresentative of events occurring at the respective locations of theleads, with at least one distinct location-specific event code beingassociated with each chamber of the heart; and transmitting thelocation-specific event codes and IEGMs to an external programmer.